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At least 343 records · Page 19Linked to original sources
PubMed1988

Altering body position affects intraocular pressure and visual function.

Intraocular pressure (IOP) can be altered by changing body position. This report describes two experiments evaluating variations in IOP, as well as neural functioning of the retina and visual cortex (as measured by pattern-reversal electroretinogram and visual evoked potential), associated with whole-body, head-down tilt. The subjects, ten per experiment, were visually normal with IOP less than 19. In the first experiment, IOP elevations were induced by varying the angle of tilt in discrete steps between +90 degrees (upright) and -90 degrees (inverted). In each position IOP was measured and significant elevations (up to 3x baseline) were noted. These elevations were maintained for 1 min during which simultaneous retinal and cortical biopotentials were measured. In the second experiment, 6 degrees head-down tilt was maintained for 2 hr during which time the IOP and both biopotentials were measured repeatedly. Our findings confirm the effect of body position of IOP, while also revealing that head-down tilt produces significant reductions in neurophysiological function at both the retinal and cortical levels. The neural effect is maximized when 6 degrees head-down tilt is maintained for 20 min.

Adult↗
PubMed1989

Prediction of visual function behind cataract using displacement threshold hyperacuity.

Visual acuity and displacement threshold hyperacuity were measured in a group of patients awaiting cataract extraction, and this was repeated several weeks subsequent to surgery. In addition, measurements were made on a group of patients with various ocular pathologies but without the presence of cataract. Displacement thresholds in the cataract group increased only slightly with the severity of the opacity. On the other hand, displacement thresholds for the pathology group showed a marked dependence upon visual acuity--the worse the acuity, the higher the threshold. This results in a clear distinction between vision loss due to optical factors (cataract) and retinal/neural factors. There was a good correlation between pre- and post-operative displacement thresholds in the cataract group, with post-operative thresholds being slightly better than pre-operative thresholds. The results suggest that this technique may offer patients a good indication of the likely quality of vision achieved following cataract extraction.

Aged↗
PubMed1993

Contrast detection in noise: a new method for assessing the visual function in cataract.

The detectability of a signal decreases in the presence of externally added visual noise. A linear relation exists between the energy of a signal at threshold and the spectral density of the added visual noise. This relation, represented by contrast detection in noise function, allows a given loss in contrast sensitivity (CS) to be attributed to an increase in the internal intrinsic noise and/or a decrease in the detection efficiency of the observer. Intrinsic noise gives a measure of the random background noise within the visual system, whereas detection efficiency is a measure of how effectively the observer utilizes the available stimulus information. Recent work shows that neural dysfunction produces a decrease in the detection efficiency, whereas optical deficits produce a change in the intrinsic noise only. We investigated whether the CS loss in cataract can be attributed to either a change in intrinsic noise, in detection efficiency, or both. Contrast detection in noise functions was measured for 10 uniocular cataract patients. Comparison between the two eyes showed no significant difference in detection efficiency, although the intrinsic noise increased significantly in the cataractous eye. The data suggest that detection efficiency may provide a measure of neural visual function behind a cataract and, conversely, that intrinsic noise provides a measure of the visual effect of the cataract itself. We discuss the implications of intrinsic noise as a measure of cataract for both clinical assessment and research.

Aged↗
PubMed1978

Modification of visual functions of the parietal lobe at early age in the monkey.

In addition to the visual pathway ending in the visual cortex, visual information is also processed in the associative areas of the cortex. We have studied the posterior parietal association area (Brodmann's area 7), and in our sample about 40% of the neurons were influenced by visual stimulation or ocular movements. The visually activated neurons in this region in normal adult monkeys have large, binocular receptive fields and they respond well to all moving visual stimuli near the animal. They do not differentiate between different patterns of visual stimuli but respond well to objects of interest, such as food, drinks, new objects, etc. Many visual neurons also respond to somatic stimulation. Preliminary experiments on two young monkeys suggest that the visual input into area 7 is strongly modified by early visual deprivation. In one monkey monocular deprivation lead to total absence of any influence from the deprived eye to area 7. No deprivation effect was observed in the lateral geniculate nucleus of the thalamus and the effect in area 7 was stronger than in the visual cortex (area 17). One monkey raised with bilateral eye closure was behaviourally blind after the opening of the eyes and remained so for the observation period of one month. In area 7 of this monkey the proportion of recording sites responsive to visual stimulation was sharply reduced. In kittens binocular deprivation is known to effect the function of the visual cortex much less than monocular deprivation. It seems possible that at early age inputs representing different sensory systems compete for influence in the associative cortical areas in the same way as there is competition between inputs from the two eyes to the visual cortex.

Age Factors↗
PubMed1998

Magnocellular visual function and children's single word reading.

Recent research has shown that reading disabled children find it unusually difficult to detect flickering or moving visual stimuli, consistent with impaired processing in the magnocellular visual stream. Yet, it remains controversial to suggest that reduced visual sensitivity of this kind might affect children's reading. Here we suggest that when children read, impaired magnocellular function may degrade information about where letters are positioned with respect to each other, leading to reading errors which contain sounds not represented in the printed word. We call these orthographically inconsistent nonsense errors "letter" errors. To test this idea we assessed magnocellular function in a sample of 58 unselected children by using a coherent motion detection task. We then gave these children a single word reading task and found that their "letter" errors were best explained by independent contributions from motion detection (i.e., magnocellular function) and phonological awareness (assessed by a spoonerism task). This result held even when chronological age, reading ability, and IQ were controlled for. These findings suggest that impaired magnocellular visual function, as well as phonological deficits may affect how children read.

Child↗
PubMed1990

[Reduced visual function in relation to compensation questions].

In cases of visual impairment due to an accident it is the ophthalmologist's task to assess the functional loss. For the purposes of legal equality norms have been established for functional loss. Differences in the assessment of disability and loss of integrity in various countries are discussed.

Blindness↗
PubMed1990

[Dynamics of visual functions in the conditions of glow and sodium lighting. II. Time of conscious reaction and visual space-hand localization].

The authors present the results of investigations performed in 20 young persons with normal sight. A trial of evaluation of the strain of the central nervous system in conditions of various kind of lighting was carried out basing on its close connection with the visual hand localization as well as with the time of the conscious reaction. Analyzed was the behaviour of the quoted functions as the time passed during the morning hours and the results of the examinations obtained in conditions of glow and sodium illumination were compared. They suggest a favourable influence of the sodium light on the discussed functions.

Adolescent↗
PubMed1975

Use of the ERG and EOG in evaluating the effect of sleep deprivation on visual function in flying personnel.

The electroretinogram (ERG) and electrooculogram (EOG) are electrophysiological tests employed in ophthalmology to diagnose degeneration or injury to the outer half of the retina, including the rods and cones of the visual system. This pilot study was undertaken to determine if sleep deprivation of more than 24 h in rated flying personnel may show an abnormality in retinal function as measured by the ERG and/or EOG. This may give insight to the visual function in flying personnel on deployment or other long missions where uninterrupted sleep may be a problem. The results of this study showed that some subjects deprived of sleep exhibited a statistically significant variance in their EOG ratios as compared to a nondeprived control group. No significant changes in ERG were detected. Principles and theory of electrophysiological testing in ophthalmology are presented.

Adult↗
PubMed1984

The effect of devascularization of the visual cortex on visual function in the rabbit.

The role of the visual cortex in brightness and pattern vision was re-examined in the rabbit. Animals were trained on both a brightness and a horizontal-vertical striation discrimination. Bilateral removal of the dura mater overlying the entire visual cortex produced no impairments in either brightness or pattern vision. When the visual cortex was devascularized by removal of the pia mater bilaterally, total loss of pattern vision was found with no impairment of brightness discrimination ability. The significance of the finding that the effects of slowly developing degenerative lesions are the same as those of surgical ablation was discussed.

Animals↗
PubMed1989

[Automatic evaluation of visual functions using a computer].

Many different tests for visual acuity, glare and contrast sensitivity, even by computer, are known. We developed a new computer system that is directed by the patient who works with a joystick. A special overlay computer program receives the answers given by the joystick, calculates the information on the screen and provides a new combination of background illumination, optotype position, color, contrast and enlargement. With this automatic test we examined cataract patients before and after the operation. After the operation the patients have better visual acuity and less sensitivity to glare- and contrast in both the dark and light.

Cataract↗
PubMed1990

Simple clinical techniques to evaluate visual function in patients with early cataract.

Among the 80 subjects who were recruited with normal retinal and neural function, 54 had cataract and a visual acuity (VA) better than 6/24. The 26 age-matched subjects had clear media. Contrast sensitivity (CS) at low and intermediate spatial frequencies was measured using the Pelli-Robson letter chart. Two measures of glare disability (GD) were obtained using the Mentor Brightness Acuity Tester (BAT) in conjunction with a logMAR VA chart and the Pelli-Robson chart. Although CS is predominantly affected at high spatial frequencies in early cataract, we found that some subjects had reduced scores on the Pelli-Robson chart. This CS loss could not be predicted from VA measurements and was particularly found in subjects with posterior subcapsular cataract. High GD scores were found in a number of subjects with relatively good VA and could not be predicted from results of VA or CS. We suggest that CS and GD measurements using the Pelli-Robson chart and the BAT provide valuable information regarding the management of patients with early cataract.

Aged↗
PubMed1985

Functional visual effects of lesions located near the optic nerve head.

Three patients with retinal lesions near or impinging on the optic nerve head are presented. Three different functional disruptions are demonstrated by quantitative layer-by-layer perimetry. In one, a patient who primarily exhibited subretinal neovascularization, inner retinal functions were anomalous; but the overlying nerve fiber bundle was as yet not affected. In the second patient, an individual with possible histoplasmosis causing an outer retinal/choroidal lesion, the overlying nerve fiber bundle was affected causing apparent retrograde changes in inner retinal function at remote visual field locations; but another aspect of optic nerve function (time-dependent response) was not anomalous. These apparently retrograde changes were essentially identical to functional changes previously demonstrated in patients with established open-angle glaucoma. In the third patient, with presumed toxoplasmosis, there were clear-out time-dependent anomalous responses consistent with optic nerve involvement, as previously reported in patients with optic neuritis. There were also modest, time-stable, nerve fiber bundle defects present in this third patient. Together, these results demonstrate that lesions in the area of the disc can have very different functional consequences, and that quantitative psychophysical techniques can elucidate these differences.

Adult↗
PubMedDate not supplied

Visual function before and after photorefractive keratectomy for myopia.

BACKGROUND: To date, Snellen visual acuity and postoperative refraction have been used to evaluate the results of photorefractive keratectomy. However, other parameters, such as contrast sensitivity function and glare, may be affected by refractive surgery and lead to unsatisfactory visual performance. This prospective study is aimed at evaluating the effect of photorefractive keratectomy on contrast sensitivity function and glare. SUBJECTS AND METHODS: Static contrast sensitivity function, dynamic contrast sensitivity function, and glare sensitivity were evaluated in 22 myopic eyes before as well as 1, 3, and 6 months after photorefractive keratectomy. The eyes tested were divided into three groups, according to the amount of myopia: group I, from -4.00 to -8.00 diopters (D); group II, from -8.25 to -11.00 D; group III, from -11.25 to -20.00 D. RESULTS: Both static and dynamic contrast sensitivity function at the intermediate spatial frequencies were altered at 1 month after photorefractive keratectomy, with a trend toward recovery at 3 and 6 months postoperatively. Glare sensitivity was not significantly affected by surgery. CONCLUSIONS: Contrast sensitivity function and glare testing may show abnormalities in the presence of optimal visual and refractive results. These tests may result especially important for the evaluation of new refractive surgical procedures.

Adolescent↗
PubMed1987

Influence of vasospasm on visual function.

In a number of patients with etiologically unexplained visual field loss, a vasospastic syndrome could be found with the help of a capillaroscopic local cooling test on the fingers. In the patients with proven vasospastic syndrome, the visual field defects were increased after a cold water test and decreased after a therapy with calcium entry blockers. General aspects of the physiology and pathophysiology of the circulation and especially of the circulation in the eye are presented.

Calcium Channel Blockers↗
PubMed1996

Visual function with monofocal versus multifocal IOLs.

PURPOSE: To assess visual outcome in four groups: one multifocal intraocular lens (IOL), one monofocal IOL, and two phakic, one older and one younger. SETTING: Department of Ophthalmology, National Health Service, Puerta de Hierro University Clinic, Madrid, Spain. METHODS: This prospective study comprised 70 aphakic eyes, 42 with a multifocal and 28 with a monofocal IOL, and 42 phakic eyes, 21 older than 60 years and 21 younger than 60 years. The phakic groups served as a double control. Main outcome measures were corrected and uncorrected distance and near visual acuities, contrast and glare sensitivity, and clinical and subjective complications. RESULTS: There were no significant differences between the monofocal and multifocal IOL groups in uncorrected or corrected distance visual acuity. Near visual acuity in the multifocal group, with and without distance correction, was significantly better than in the monofocal group. Near vision with addition was similar between the two IOL groups. There were no significant differences between the monofocal and multifocal IOL groups in contrast sensitivity at the 96 and 50% thresholds. Between-group differences of less than one Regan line were found at the 25 and 11% thresholds. The phakic groups had better contrast sensitivity. The older phakic group's results were closer to those of the IOL groups. There were no significant complications. CONCLUSION: Distance acuity and contrast sensitivity were similar in the monofocal and multifocal IOL groups; however, the multifocal group had significantly better near acuity. The younger phakic group had significantly better contrast sensitivity than the other groups.

Adult↗
PubMedDate not supplied

[The effect of anti-glaucoma surgery on the visual function in patients with primary glaucoma].

Examinations of the visual field in 25 patients with Stages I and II primary open-angle glaucoma have shown that in the majority of cases surgery results in improvement of stabilization of the visual field status in respect of all its parameters (retinal sensitivity threshold, deficiency of the field and sensitivity). Increase of the number of defects and reduction of the retinal ability to discern light were observed in 5 patients: in 2 with postoperative hypotension and 3 with progressive cataracts.

Adult↗